Background. Prostate cancer has become the most frequently diagnosed malignancy in American men, particularly the African American population which experiences the highest rates in the world. It is probable that a number of dietary factors modulate risk. The Health Professionals Follow-Up Study has detected a significant reduction in prostate cancer risk with the consumption of tomato products. Several additional lines of preliminary evidence derived by our group support the hypothesis that tomato products may reduce risk. The biologically active substances in tomatoes that may influence the prostate are unknown. One possibility is the carotenoid lycopene. Higher serum concentrations of lycopene are associated with reduced prostrate cancer risk in the Physicians Health Study. Lycopene is the most common carotenoid in the human prostate and has antiproliferative effects on prostate cells in vitro. Hypothesis. We hypothesize that diets supplemented with tomato products or lycopene inhibit de novo prostate carcinogenesis, prostate tumor growth rates, and metastases in well characterized rodent models. Experimental Approach. The effects of diets supplemented with tomato powder, tomato lipophilic extract, or lycopene on prostate carcinogenesis will be evaluated in five models. (1). NMU/androgen-induced rat prostate carcinogenesis. (2). The growth rate of the well differentiated, slow growing and androgen sensitive Dunning R3327H prostate adenocarcinoma in rats. (3). Metastatic spread of the MatLyLu poorly differentiated and androgen independent prostate adenocarcinoma in rats. (4). The growth rate of the human poorly differentiated, androgen resistant, and p53 mutant PC-3 prostate adenocarcinoma in SCID mice. (5). The growth rate of the human, poorly differentiated, hormone dependent, and p53 normal LNCaP human prostate adenocarcinoma in SCID mice. Relevance. These studies will provide critical data for the understanding of prostate cancer etiology and prevention as well as the potential development of a new chemopreventive agent.